This invention relates to a tensioner lever used for guiding and tensioning a chain or belt in a transmission device. The transmission device may be a device that transmits power from a driving sprocket to a driven sprocket through an endless chain or toothed belt engaged with both sprockets, or a device that transmits power from a driving pulley to a driven pulley by an endless belt engaged with both pulleys.
Various machines, for example internal combustion engines, include a transmission device that transmits power through an endless chain, a belt or the like that travels in a closed loop. In such a transmission device, a tensioner lever, as shown in FIG. 9, FIG. 10, or FIG. 11, is used to apply appropriate tension to the belt or chain while in sliding contact with the belt or chain. The tensioner lever also functions to prevent vibration of the chain or belt, including vibration in the plane of the loop and lateral vibration.
Tensioner lever A, shown in FIG. 9, is a two-piece structure comprising a shoe A10, composed of a resin material for engagement with a portion of a travelling chain, and an aluminum die cast base member A20. The base member must be sufficiently strong to hold the shoe A10. (See Japanese patent application No. Hei 11-155672.)
Tensioner lever B, shown in FIG. 10, is a two-piece structure comprising a shoe B10 composed of a resin material for engagement with a portion of a travelling chain, and a steel plate B20 for holding the shoe B10. (see Japanese patent application No. 2001-69238.) The strength of the steel plate is also important in this tensioner lever.
Tensioner lever C, shown in FIGS. 11(a) and 11(b), is a two-piece structure comprising a shoe C10 composed of a resin material for engagement with a portion of a travelling chain, and a base member C20, composed of a resin reinforced with glass fiber or the like, for holding the shoe C10. Here again, the strength of the base member is important.
Each of these conventional tensioner levers is in the form of a two-piece structure comprising a shoe and a base member or plate. The properties of the shoe must be such as to permit sliding contact with the chain as the moves in the longitudinal direction along the shoe, while resisting wear. The base member or plate must have sufficient mechanical strength to hold the shoe. By appropriate selection of materials for the respective members, properties such as the sliding contact properties, wear resistance, mechanical strength and the like, required for the tensioner lever, are combined with one another with a high degree of compatibility. However, these conventional tensioner levers have the following problems.
In the tensioner lever A shown in FIG. 9, the strength of the base member A20, which is made of die cast aluminum, is low, and the walls of the base member A20 must be made relatively thick to achieve sufficient rigidity. Even if the base member A20 is molded with unnecessary portions cut out, it occupies a large volume, and therefore it is not possible to produce a practical, light weight lever having this structure. Furthermore, the production cost, especially the cost of materials and molding, is high. In addition, since a plurality of hooks A11 is required for securing the shoe A10 to the base member A20 assembly of the shoe, assembly is difficult.
In the tensioner lever B shown in FIG. 10, in which a steel plate B20 is used as a base member, even though the wall thickness of the plate can be less than that of the die cast aluminum base member of FIG. 9, and even though the shoe is formed with ribbed sidewalls, in order to achieve sufficient strength, the weight of the steel plate is necessarily relatively high. Consequently, in this case it is also impossible to achieve a practical, light weight lever. Furthermore, in order to secure the plate member B20 on the shoe B10 reliably, it is necessary to match the width of the plate-inserting slot B11 on the back of the shoe B10 accurately with the thickness of the plate member B20. Thus high molding accuracy is required for producing the shoe B10. It is also difficult to insert the plate member B20 into the shoe B10.
In the tensioner lever C shown in FIG. 11, since all the parts are composed of resin, the tensioner lever C is lighter than the tensioner levers of FIGS. 9 and 10. However, because of the complex shape of the base member C20, injection molding of the base member is time-consuming, and the production cost of the tensioner lever C is substantially the same as that of the tensioner lever utilizing a die cast aluminum base. Furthermore, as mentioned previously, because a plurality of hooks C11 is required for securing the base member C20 and the shoe C10, assembly time is relatively high.
Further, in recent years, environmental concerns have brought about requirements for recycling of automobile parts. However, in recycling the above-described conventional tensioner levers, separation of the shoes from the base members or plates is complex, and consequently, recycling is difficult.
As a result of as study of tensioner levers using advanced methods of structure analysis and stress analysis, the inventor has made a surprising determination. Contrary to the common belief that the shoe in a tensioner lever must both play a chain guiding role and also contribute to the overall mechanical strength of the lever, it has been found that the mechanical strength of the tensioner lever is almost entirely a function of the base member or the plate member, and that the shoe plays only a guiding role for the chain or belt.